103 research outputs found
Chemical enrichment in very low-metallicity environments: Bootes I
We present different chemical evolution models for the ultrafaint dwarf
galaxy Bootes I. We either assume that the galaxy accretes its mass through
smooth infall of gas of primordial chemical composition (classical models) or
adopt mass accretion histories derived from the combination of merger trees
with semi-analytical modelling (cosmologically-motivated models). Furthermore,
we consider models with and without taking into account inhomogeneous mixing in
the ISM within the galaxy. The theoretical predictions are then compared to
each other and to the body of the available data. From this analysis, we
confirm previous findings that Bootes I has formed stars with very low
efficiency but, at variance with previous studies, we do not find a clear-cut
indication that supernova explosions have sustained long-lasting galactic-scale
outflows in this galaxy. Therefore, we suggest that external mechanisms such as
ram pressure stripping and tidal stripping are needed to explain the absence of
neutral gas in Bootes I today.Comment: 13 pages, 11 figures, accepted for publication in MNRA
On the link between nuclear star cluster and globular cluster system mass, nucleation fraction and environment
We present a simple model for the host mass dependence of the galaxy
nucleation fraction (), the galaxy's nuclear star cluster (NSC) mass
and the mass in its surviving globular clusters (). Considering the
mass and orbital evolution of a GC in a galaxy potential, we define a critical
mass limit () above which a GC can simultaneously in-spiral to the
galaxy centre due to dynamical friction and survive tidal dissolution, to build
up the NSC. The analytic expression for this threshold mass allows us to model
the nucleation fraction for populations of galaxies. We find that the slope and
curvature of the initial galaxy size-mass relation is the most important factor
(with the shape of the GC mass function a secondary effect) setting the
fraction of galaxies that are nucleated at a given mass. The well defined
skew-normal observations in galaxy cluster populations are
naturally reproduced in these models, provided there is an inflection in the
{initial} size-mass relation at . Our
analytic model also predicts limits to the and relations which bound the scatter of the observational data.
Moreoever, we illustrate how these scaling relations and vary if the
star cluster formation efficiency, GC mass function, galaxy environment or
galaxy size-mass relation are altered. Two key predictions of our model are: 1)
galaxies with NSC masses greater than their GC system masses are more compact
at fixed stellar mass, and 2) the fraction of nucleated galaxies at fixed
galaxy mass is higher in denser environments. That a single model framework can
reproduce both the NSC and GC scaling relations provides strong evidence that
GC in-spiral is an important mechanism for NSC formation.Comment: 17 pages, 20 figures. Accepted for publication in MNRA
Halpha Kinematics of S4G Spiral Galaxies - III. Inner rotation curves
We present a detailed study of the shape of the innermost part of the
rotation curves of a sample of 29 nearby spiral galaxies, based on high angular
and spectral resolution kinematic Halpha Fabry-Perot observations. In
particular, we quantify the steepness of the rotation curve by measuring its
slope dRvc(0). We explore the relationship between the inner slope and several
galaxy parameters, such as stellar mass, maximum rotational velocity, central
surface brightness ({\mu}0), bar strength and bulge-to-total ratio. Even with
our limited dynamical range, we find a trend for low-mass galaxies to exhibit
shallower rotation curve inner slopes than high-mass galaxies, whereas steep
inner slopes are found exclusively in high-mass galaxies. This trend may arise
from the relationship between the total stellar mass and the mass of the bulge,
which are correlated among them. We find a correlation between the inner slope
of the rotation curve and the morphological T-type, complementary to the
scaling relation between dRvc(0) and {\mu}0 previously reported in the
literature. Although we find that the inner slope increases with the Fourier
amplitude A2 and decreases with the bar torque Qb, this may arise from the
presence of the bulge implicit in both A2 and Qb. As previously noted in the
literature, the more compact the mass in the central parts of a galaxy (more
concretely, the presence of a bulge), the steeper the inner slopes. We conclude
that the baryonic matter dominates the dynamics in the central parts of our
sample galaxies.Comment: 11 pages, 11 figures, accepted for publication in MNRA
Young, metal-enriched cores in early-type dwarf galaxies in the Virgo cluster based on colour gradients
Early-type dwarf galaxies are not simply featureless, old objects, but were
found to be much more diverse, hosting substructures and a variety of stellar
population properties. To explore the stellar content of faint early-type
galaxies, and to investigate in particular those with recent central star
formation, we study colours and colour gradients within one effective radius in
optical (g-r) and near-infrared (i-H) bands for 120 Virgo cluster early types
with -19 mag < < -16 mag. Twelve galaxies turn out to have blue cores,
when defined as g-r colour gradients larger than 0.10 mag/, which
represents the positive tail of the gradient distribution. For these galaxies,
we find that they have the strongest age gradients, and that even outside the
blue core, their mean stellar population is younger than the mean of ordinary
faint early types. The metallicity gradients of these blue-cored early-type
dwarf galaxies are, however, in the range of most normal faint early types,
which we find to have non-zero gradients with higher central metallicity. The
blue central regions are consistent with star formation activity within the
last few 100 Myr. We discuss that these galaxies could be explained by
environmental quenching of star formation in the outer galaxy regions, while
the inner star formation activity has continued
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